Hot glue, also known as hot melt adhesive or hot melt, is used in a wide variety of industrial applications for adhesively bonding materials or products with each other.
A state-of-the-art hot glue application system (see FIG. 1) generally comprises a melter 100, one or more heatable feed hoses 200, and one or more heatable application valves 300.
The melter 100 comprises the following components:
A heatable tank 110, into which the hot glue is charged in the solid state in granulated form or block form. The heatable tank 110 liquefies the hot glue and serves as a hot glue reservoir. A heater 111, which can have one or more heating zones, heats the tank to a sufficiently high temperature to liquefy the hot glue. To maintain the operating temperature, the actual temperature is determined for the automatic control system by one or more temperature sensors 112, depending on the number of heating zones.
A pump 120, which pumps the melted hot glue to the connected consumers.
A pressure relief valve 130, which relieves the consumer side when the operating pressure is exceeded and returns the hot glue to the tank 110
A filter 140, which prevents particles of a size that could lead to clogging of the application valves from reaching the consumer side.
A distributor 150, which has several hydraulic connections, to which heatable feed hoses can be connected for supplying hot glue.
An electronic control unit 170 with a multizone automatic temperature control and monitoring unit 171 and a user interface and display unit 172. The multizone automatic temperature control and monitoring unit 171 provides for attaining and maintaining the set temperature of the tank heating zones and, via several external connections, for attaining and maintaining the set temperature for the connected heatable feed hoses and heatable application valves and for monitoring them.
The heatable feed hoses 200 are for supplying the application valves 300 with liquid hot glue. They are heated by a heater 210 to maintain the hot glue supplied by the melter 100 in the liquid state. To maintain the operating temperature, the actual temperature is determined by the temperature sensor 112 and sent to the control unit 170 for automatic control.
The heatable application valves 300 have an electrically or electropneumatically operated closing plug and a nozzle for metering and positioning a portion of hot glue 20 to be applied to the product to be bonded. They are heated by a heater 310 in order to liquefy the hot glue supplied by the melter 100 through the heatable feed hoses to such an extent that it can be applied through the nozzle with the required viscosity and temperature for the given application. To maintain the operating temperature, the actual temperature is determined by the temperature sensor 320 and supplied to the control unit 170 for automatic control.
Depending on the application, a variable number of heatable feed hoses 200 and heatable application valves 300 with variable heating capacity and automatic control response can be connected to the melter 100. The configuration of the hot glue application system can also be frequently changed after the initial installation if different products are being bonded, the hot glue is changed, or a failed component is replaced by a component with different characteristics from the failed component.
The heating time of the hot glue application system and the control deviation of the operating temperature from the adjusted set value of the individual heating circuits are important application parameters, which directly affect productivity and operational reliability of such systems. To optimize the automatic control response, it is necessary that the multizone automatic temperature control and monitoring unit 171 has at its disposal the automatic control parameters, such as delay time and amplification factor, as well as other technical data, such as heating capacity and maximum temperatures, of all connected components.
It is well known that the multizone automatic temperature control and monitoring unit 171 should be designed in such a way that the automatic control parameters for the different connected components can be input manually.
However, the manual input of automatic control parameters is burdensome and prone to error when the components, the type of glue, or the products to be bonded are frequently changed.
Self-optimizing algorithms in digital controllers, which are started manually, cyclically, or during initialization of the control and automatically determine the automatic control parameters by test procedures, are state of the art. However, these algorithms are successful only if, during connection of a heating circuit, the deviation of the automatic control parameters from the current values is automatically detected, or if, during a reconnection, an optimization cycle is manually initiated in each case. The limiting values for the heating capacity and the operating temperature cannot be determined by this method. This is critical especially when a defect develops in the heating circuit during the operation or a defective component is connected, since the control unit then adjusts the automatic control response to the redetermined parameters without triggering an alarm. This can have a negative effect on the quality of the hot glue application and, if the maximum temperatures are exceeded, it can lead to serious safety risks. Furthermore, without knowledge of additional technical data on the connected components, the algorithms offer no possibility of optimizing the behavior of the hot glue application system as a whole, such as power consumption or total heating time.
Therefore, in previously known hot glue application systems, the electronic control unit 170 operates either with permanently set mean automatic control parameters and the maximum values for the heating capacity and operating temperature or with self-optimization that is to be manually initiated.
Furthermore, in previously known hot glue application systems, only the temperature sensors are monitored for short circuit and sensor failure, since as a rule only one type is used, whose data are permanently stored in the electronic control unit. The heaters are not monitored, since the manual input of the heating parameters is too burdensome, and the additional installation of sensors, such as current sensors, breaks the cost limits. This presents problems if, for example, a defective heater is replaced by a heater with different characteristics.
Another problem is that all of the components that are used have only a limited service life, and the failure of only one component can lead to the failure of the whole hot glue application system.
One well-known method for increasing the availability of an automated production system consists in preventive maintenance of the components of such a system. In this method, preventive repair or preventive component replacement is carried out on the basis of the trouble-free operating time that can be expected, which is obtained from statistical analysis or empirical testing. A prerequisite for organizing the preventive maintenance is the recording and availability of the current operating time of the individual components. To this end, all events that cause the operating time of the individual components to deviate from the operating time of the whole system must be documented in a logbook by manual entry, which is labor-intensive and prone to error. Therefore, in previously known hot glue application systems, only the operating time of the melter 100 is monitored. The operating time of the connected components is not automatically monitored.
In addition, in the previously known hot glue application systems, when limiting parameters in the components are exceeded, this is not recorded. Therefore, this information is not available for the diagnosis.